1. Field of the Invention
The present invention generally relates to a ferrule for an optical connector used in a connecting portion between optical fibers or a connecting portion of an optical module such as an optical semiconductor, and more particularly, it relates to an MT connector ferrule.
2. Description of the Related Art
FIG. 9 shows an example of a conventional ferrule for an optical connector (referred to as xe2x80x9cferrulexe2x80x9d). The ferrule shown in FIG. 9 is used for interconnecting optical fibers or for connecting an optical fiber to a connecting portion of an optical module by attaching the ferrule to an end of a coated optical fiber A having four bare fibers C. As shown in FIG. 9, the ferrule is provided with an insertion opening B through which the bare fibers C (from which the coating is removed) are inserted. The bare fibers C are further inserted into two or more fiber holes D. Guide grooves E are provided for guiding the bare fibers C into each of the fiber holes D. An injection port F is provided for injecting adhesive for securing the coated optical fiber A to the ferrule. Guide pin holes G are provided for insertion of guide pins (not shown) for positioning two ferrules abutting against each other.
In order to assemble an optical connector by using the ferrule shown in FIG. 9, the bare fibers C (from which the coating is removed) are inserted through the insertion opening B into respective guide grooves E. The bare fibers C may be inserted into the fiber holes D by pushing the coated optical fiber A along the guide grooves E in the direction toward the fiber holes D. The adhesive is injected through the injection port F to secure the coated optical fiber A to the ferrule.
The conventional ferrule shown in FIG. 9 has the following disadvantages.
(1) As shown in FIG. 10, flat portions J exist between both end guide grooves E in an arrangement direction (width-wise direction) and inner wall surfaces H of the ferrule. When the bare fibers C are dropped into the guide grooves E from above, one of both end bare fibers C may ride on the flat portion J, thereby making it difficult to drop all of the bare fibers C into the respective guide grooves E. Although a condition that the right end bare fiber C rides on the right end flat portion J is shown, the left end bare fiber C may ride on the left end flat portion J.
(2) As shown in FIG. 10, the inner wall surfaces H of the ferrule are shown to rise vertically from the flat portions J. As a result, when the adhesive is injected through the injection port F (see FIG. 9), the adhesive may be cured while bubbles remain in corners K between the flat portions J and the inner wall surfaces H. In such a case, since the bubbles are expanded or contracted due to change in surrounding temperature, optical property and adhesion strength are deteriorated.
In order to eliminate the disadvantages of the ferrule shown in FIG. 9, a ferrule as shown in FIG. 11 has been proposed. In the ferrule shown in FIG. 11, the inner wall surfaces H of the ferrule rise vertically from lateral edges of both end guide grooves E to eliminate flat portions J as shown in FIG. 10. However, the ferrule shown in FIG. 11 has the disadvantages provided below.
(1) A distance between the both end guide grooves E is substantially equal to the opposed inner wall surfaces H. Since the inner wall surfaces H are not spaced apart from each other adequately, it is difficult to insert the bare fibers C between them, thereby worsening the operability.
(2) Since a contact area between the adhesive and the ferrule is decreased, the adhesion strength is reduced, and consequently the pulling strength for the fiber becomes insufficient.
FIG. 12 shows a further example of a conventional ferrule. The ferrule shown in FIG. 12 is also used for interconnecting optical fibers or for connecting an optical fiber to a connecting portion of an optical module by attaching the ferrule to an end of a coated optical fiber A having four bare fibers C. As shown in FIG. 12, the ferrule is provided with an insertion opening B through which the bare fibers C (from which the coating is removed) are inserted. Two or more fiber holes D1 are provided for inserting the bare optical fibers C. Minute holes D2 are provided for inserting distal ends of the bare fibers C. Guide grooves E are provided for guiding the bare fibers into the each fiber holes D1. A filling space L is provided to be filled by adhesive for securing the coated optical fiber A to the ferrule. The adhesive M (FIG. 13B) is inserted through an injection port F to fill in the filling space L. Guide pin holes G are provided to insert guide pins (not shown) for positioning two ferrules abutting against each other.
In order to assemble an optical connector by using the ferrule shown in FIG. 12, as shown in FIG. 13A, the bare fibers C (from which the coating is removed) are inserted through the insertion opening B. The inserted bare fibers C are dropped into respective guide grooves E. As shown in FIG. 13B, the coated optical fiber A is pushed into the ferrule until the a predetermined portion of the bare fibers C protruds from an end face N of the ferrule by a predetermined lengths. Thereafter, the adhesive M is injected into the filling space L (see FIG. 13A) through the injection port F, thereby securing the coated optical fiber A to the ferrule.
The conventional ferrule shown in FIG. 12 had the following disadvantage discussed below.
(1) As shown in FIG. 13A, a forward inner surface O of the filling space L is a vertical surface extending vertically from a leading edge P of the injection port F to start points Q of the fiber holes D1. The volume of the filling space L is small and thus the filling amount of the adhesive M (see FIG. 13B) becomes insufficient. Further, since the guide grooves E terminate at the inner surface O of the filling space L, as shown in FIG. 13B, the amount of the adhesive M filled around the bare fibers C is very small. In addition, since the diameters of the fiber holes D, are small, the adhesive M may not be filled in the fiber holes. For these reasons, pulling strength of the fiber becomes insufficient, and a fiber securing force is reduced because of deterioration of adhesive particularly due to change in temperature and a high humidity environment.
In order to eliminate this problem, as shown in FIG. 14, a ferrule in which the injection port F is extended in the fiber inserting direction to increase the volume of the filling space L has been proposed. However, the ferrule shown in FIG. 14 has the following disadvantages.
(1) Since the injection port F is positioned near the end face N of the ferrule, the symmetry in the vicinity of the end face N is worsened. As a result, it is difficult to achieve the accuracy at the sub-micron level required for the optical connector ferrule.
(2) Since a ratio of cavity to the entire ferrule is increased because of increased volumes of the injection port and the filling space, physical strength of the ferrule is decreased. As a result, a camber may be generated in the ferrule due to change in surrounding temperature.
In one embodiment, the invention provides an optical connector ferrule comprising an insertion opening through which one end of a coated optical fiber with the coating removed is inserted. The ferrule further comprises guide grooves for guiding the bare fibers inserted through the insertion opening, fiber holes into which the bare fibers guided by the guide grooves are inserted. The ferrule further comprises an injection port through which adhesive for securing the coated optical fiber to the ferrule is injected. A guide surface or guide surfaces for guiding the bare fibers to guide groove is or are formed at one or both sides of the guide grooves in a width-wise direction thereof, and each guide surface is inclined downwardly toward the corresponding guide grooves.
According to another embodiment, the invention provides an optical connector ferrule comprising an insertion opening through which one end of a coated optical fiber with the coating removed is inserted. The ferrule further compries guide grooves for guiding the bare fibers inserted through the insertion opening, and fiber holes into which the bare fibers guided by the guide grooves are inserted. The ferrule further comprises an injection port through which adhesive for securing the coated optical fiber to the ferrule is injected, and a filling space into which the adhesive injected through the injection port is filled. An enlarged portion extending from a distal end of the injection port is formed in front of the filling space in an optical fiber inserting direction.
According to a further embodiment, the invention provides an optical connector ferrule comprising an insertion opening through which one end of a coated optical fiber with the coating removed is inserted. The ferrule further comprises guide grooves for guiding the bare fibers inserted through the insertion opening, and fiber holes into which the bare fibers guided by the guide grooves are inserted. The ferrule further comprises an injection port through which adhesive for securing the coated optical fiber to the ferrule is injected, and a filling space into which the adhesive injected through the injection port is filled. An enlarged portion extending from a distal end of the injection port is formed in front of the filling space in an optical fiber inserting direction, and a ceiling surface of the enlarged portion is inclined downwardly forwardly from the injection port.